*,
*:before,
*:after {
  box-sizing: border-box;
  margin    : 0;
  padding   : 0;
}


$vertPad: 80px;
$sidePad: 70px;

$numOfEls: 5;
$elMrg   : 1%;

$initAT           : 1s;
$initDelayStep    : 0.1s;
$fullInitAT       : $initAT+$initDelayStep * ($numOfEls - 1);
$moveAT           : 0.6s;
$expandAT         : 0.7s;
$expandDelay      : 0.1s;
$bgScaleAT        : 0.8s;
$fadeoutAT        : $moveAT+$expandAT/2;
$indexHoverAT     : 0.5s;
$closeBtnAT       : 0.3s;
$closeBtnLineDelay: 0.15s;
$fullExpandAT     : $moveAT+$expandDelay+$expandAT;
$contentFadeinAT  : 0.5s;

@mixin elHover {
  .el:hover & {
    @content;
  }
}

@mixin elActive {
  .el.s--active & {
    @content;
  }
}

@mixin contInactive {
  .cont.s--inactive & {
    @content;
  }
}

@mixin contElActive {
  .cont.s--el-active & {
    @content;
  }
}

.cont {
  position: relative;
  overflow: hidden;
  height  : 100vh;
  padding : $vertPad $sidePad;

  &__inner {
    position: relative;
    height  : 100%;

    &:hover .el__bg:after {
      opacity: 1;
    }
  }
}

.el {
  $elW     : (100% - $elMrg * ($numOfEls - 1)) / $numOfEls;
  $elMrgRel: percentage($elMrg / $elW);

  position   : absolute;
  left       : 0;
  top        : 0;
  width      : $elW;
  height     : 100%;
  background : #252525;
  transition : transform $moveAT $expandAT, width $expandAT, opacity $moveAT $expandAT, z-index 0s $moveAT + $expandAT;
  will-change: transform, width, opacity;

  &:not(.s--active) {
    cursor: pointer;
  }

  &__overflow {
    overflow: hidden;
    position: relative;
    height  : 100%;
  }

  &__inner {
    overflow  : hidden;
    position  : relative;
    height    : 100%;
    transition: transform $initAT;

    @include contInactive {
      transform: translate3d(0, 100%, 0);
    }
  }

  &__bg {
    position   : relative;
    width      : calc(100vw - #{$sidePad * 2});
    height     : 100%;
    transition : transform $moveAT $expandAT;
    will-change: transform;

    &:before {
      content            : "";
      position           : absolute;
      left               : 0;
      top                : -5%;
      width              : 100%;
      height             : 110%;
      background-size    : cover;
      background-position: center center;
      transition         : transform $initAT;
      transform          : translate3d(0, 0, 0) scale(1);

      @include contInactive {
        transform: translate3d(0, -100%, 0) scale(1.2);
      }

      @include elActive {
        transition: transform $bgScaleAT;
      }
    }

    &:after {
      $opacityAT: 0.5s;

      content   : "";
      z-index   : 1;
      position  : absolute;
      left      : 0;
      top       : 0;
      width     : 100%;
      height    : 100%;
      background: rgba(0, 0, 0, 0.3);
      opacity   : 0;
      transition: opacity $opacityAT;

      @include contElActive {
        transition: opacity $opacityAT $fullExpandAT;
        opacity   : 1 !important;
      }
    }
  }

  &__preview-cont {
    z-index        : 2;
    display        : flex;
    justify-content: center;
    align-items    : center;
    position       : absolute;
    left           : 0;
    top            : 0;
    width          : 100%;
    height         : 100%;
    transition     : all 0.3s $fullInitAT - 0.2s;

    @include contInactive {
      opacity  : 0;
      transform: translateY(10px);
    }

    @include contElActive {
      opacity   : 0;
      transform : translateY(30px);
      transition: all 0.5s;
    }
  }

  &__heading {
    color         : #fff;
    text-transform: uppercase;
    font-size     : 18px;
  }

  &__content {
    z-index       : -1;
    position      : absolute;
    left          : 0;
    top           : 0;
    width         : 100%;
    height        : 100%;
    padding       : 30px;
    opacity       : 0;
    pointer-events: none;
    transition    : all 0.1s;

    @include elActive {
      z-index       : 2;
      opacity       : 1;
      pointer-events: auto;
      transition    : all $contentFadeinAT $fullExpandAT;
    }
  }

  &__text {
    text-transform: uppercase;
    font-size     : 40px;
    color         : #fff;
  }

  &__close-btn {

    z-index       : -1;
    position      : absolute;
    right         : 10px;
    top           : 10px;
    width         : 60px;
    height        : 60px;
    opacity       : 0;
    pointer-events: none;
    transition    : all 0s $closeBtnAT + $closeBtnLineDelay;
    cursor        : pointer;

    @include elActive {
      z-index       : 5;
      opacity       : 1;
      pointer-events: auto;
      transition    : all 0s $fullExpandAT;
    }

    &:before,
    &:after {
      content   : "";
      position  : absolute;
      left      : 0;
      top       : 50%;
      width     : 100%;
      height    : 8px;
      margin-top: -4px;
      background: #fff;
      opacity   : 0;
      transition: opacity 0s;

      @include elActive {
        opacity: 1;
      }
    }

    &:before {
      transform: rotate(45deg) translateX(100%);

      @include elActive {
        transition: all $closeBtnAT $fullExpandAT cubic-bezier(.72, .09, .32, 1.57);
        transform : rotate(45deg) translateX(0);
      }
    }

    &:after {
      transform: rotate(-45deg) translateX(100%);

      @include elActive {
        transition: all $closeBtnAT $fullExpandAT + $closeBtnLineDelay cubic-bezier(.72, .09, .32, 1.57);
        transform : rotate(-45deg) translateX(0);
      }
    }
  }

  &__index {
    overflow   : hidden;
    position   : absolute;
    left       : 0;
    bottom     : $vertPad * -1;
    width      : 100%;
    height     : 100%;
    min-height : 250px;
    text-align : center;
    font-size  : 100vw / $numOfEls;
    line-height: 0.85;
    font-weight: bold;
    transition : transform $indexHoverAT, opacity $moveAT/2 $expandAT + $expandDelay + $moveAT;
    transform  : translate3d(0, 1vw, 0);

    @include elHover {
      transform: translate3d(0, 0, 0);
    }

    @include contElActive {
      transition: transform $indexHoverAT, opacity $moveAT/2;
      opacity   : 0;
    }

    &-back,
    &-front {
      position: absolute;
      left    : 0;
      bottom  : 0;
      width   : 100%;
    }

    &-back {
      color     : #2f3840;
      opacity   : 0;
      transition: opacity $indexHoverAT/2 $indexHoverAT/2;

      @include elHover {
        transition: opacity $indexHoverAT/2;
        opacity   : 1;
      }
    }

    &-overlay {
      overflow  : hidden;
      position  : relative;
      transform : translate3d(0, 100%, 0);
      transition: transform $indexHoverAT 0.1s;
      color     : transparent;

      &:before {
        content   : attr(data-index);
        position  : absolute;
        left      : 0;
        bottom    : 0;
        width     : 100%;
        height    : 100%;
        color     : #fff;
        transform : translate3d(0, -100%, 0);
        transition: transform $indexHoverAT 0.1s;
      }

      @include elHover {
        transform: translate3d(0, 0, 0);

        &:before {
          transform: translate3d(0, 0, 0);
        }
      }
    }
  }

  @for $i from 0 to $numOfEls {
    &:nth-child(#{$i + 1}) {
      $x              : (100% + $elMrgRel) * $i;
      transform       : translate3d($x, 0, 0);
      transform-origin: $x + 50% 50%;

      @include contElActive {

        &:not(.s--active) {
          transform : scale(0.5) translate3d($x, 0, 0);
          opacity   : 0;
          transition: transform $fadeoutAT, opacity $fadeoutAT;
        }
      }

      .el__inner {
        transition-delay: $initDelayStep * $i;
      }

      .el__bg {
        transform: translate3d($elW * $i * -1, 0, 0);

        &:before {
          transition-delay: 0.1s * $i;
          background-image: url('https://s3-us-west-2.amazonaws.com/s.cdpn.io/142996/onepgscr-#{$i + 3}.jpg');
        }
      }
    }
  }

  &:hover {

    .el__bg:after {
      opacity: 0;
    }
  }

  &.s--active {
    z-index   : 1;
    width     : 100%;
    transform : translate3d(0, 0, 0);
    transition: transform $moveAT, width $expandAT $moveAT + $expandDelay, z-index 0s;

    .el__bg {
      transform : translate3d(0, 0, 0);
      transition: transform $moveAT;

      &:before {
        transition-delay: $moveAT;
        transform       : scale(1.1);
      }
    }
  }
}

.icon-link {
  position: absolute;
  left    : 5px;
  bottom  : 5px;
  width   : 32px;

  img {
    width         : 100%;
    vertical-align: top;
  }

  &--twitter {
    left : auto;
    right: 5px;
  }
}